The present invention relates to the field of medical simulation and, in particular, it concerns a device and method for achieving simulation of a Doppler ultrasound examination.
It is well known that a complete ultrasound interrogation of any part of the cardiovascular system includes both imaging of the physical structure of the tissues being examined, as well as interrogation of the nature of blood flow through the blood vessels or heart valves being examined. Two dimensional imaging is achieved by means of "B-mode" ultrasound imaging, in which a two-dimensional gray-scale image of the tissues being examined is generated. However, the nature of blood flow (i.e. it's velocity), cannot be depicted by B-mode imaging, and for this purpose C-mode and D-mode ultrasound imaging, both of which utilize the Doppler principle, are used.
Doppler ultrasound uses the Doppler effect created by moving objects, such as blood cells which are flowing through a blood vessel, to depict flow information. The Doppler effect consists of an acquired change in frequency of an ultrasound wave which occurs when the ultrasound wave is reflected off of a moving object. If the initial frequency of the ultrasound wave is known, then the velocity of the moving reflector can be inferred from the Doppler shift acquired by the reflected wave. By measuring the Doppler shift acquired by ultrasound waves focused on a blood vessel, a "Doppler spectral graph" can be generated, which plots the velocity of blood flow against time for a single location in the blood vessel. This is known as D-mode ultrasound imaging.
In C-Mode (or Color Flow) the Doppler shift created by the movement of blood cells at a particular location in a B-mode image is depicted on a color scale at that location. The location on the B-mode image at which C-mode color data is mapped is demarcated by a graphic box, also referred to as a "color box", which is positioned by the user at the desired location on the B-mode image. C-mode imaging can thus depict blood velocity data for a multitude of points simultaneously, and generate a dynamic color image which is displayed over the B-Mode (gray-scale) image of the same area.
To perform D-Mode imaging, the user first marks the desired measurement location (which is also referred to as the "sample volume" or "gate") with a cursor on the B-Mode or C-Mode image. D-mode imaging is then initiated by the user by activating the appropriate control on the ultrasound machine. Additional manipulations, such as marking the estimated direction of blood flow and adjusting the ultrasound gain, compress and/or aliasing limit, are manually performed by the operator so as to optimize the spectral Doppler waveform. FIG. 1 shows an example of a D-mode Doppler spectral graph (in the lower half of the figure) and the corresponding B-mode image and sample volume at which the spectral graph was acquired (in the upper half of the figure).
As the measured Doppler frequency shift at any instant in time is usually within the audible range, the measured signal is also depicted as an audible sound of that frequency. This sound helps the user to optimize the sample volume position within a blood vessel, to differentiate between different vessels, and to identify the presence of pathology.
Performance of a Doppler ultrasound examination is thus complex, and requires that the user be highly proficient at hand-eye coordination when manipulating the ultrasound probe and the many controls involved. In addition, the user must be familiar with a wide range of pathologies, and must understand the physical principles behind the Doppler shift and its measurement by means of ultrasound. Intensive training, and much experience, are therefore required before an ultrasound technician, or a physician who uses ultrasound, achieves competency in performing Doppler ultrasound examinations.
The training of physicians and technicians in the use of Doppler ultrasound techniques is currently performed on actual patients. This system suffers from several limitations:
1. The time available for hands-on training on a given patient or pathology is limited. As such, students are not free to spend as much time as they may require on a particularly difficult or interesting case, particularly if the case is an urgent one. In addition, experimentation by the trainee with different ways of performing the same examination is not always feasible. PA0 2. The level of training varies depending on the teacher and the availability of patients. PA0 3. Rarer pathologies are often not encountered at all during training. PA0 4. Hands-on training can only take place in clinical settings and at times when patients are available, rather than at times and locations which are most convenient to the teacher and trainee. PA0 1. There is no consistency from exam to exam. One pupil may thus get a very difficult case, whereas another will have an easier one. PA0 2. The scoring of an exam by an examiner is subjective. PA0 3. Appropriate patients with varied pathologies may not be available for examination purposes.
Furthermore, the accreditation process for sonographers is problematic when real patients must be used, for the following reasons:
There is therefore a need for a method of realistically simulating Doppler ultrasound examinations, such that trainee sonographers can perform Doppler ultrasound examinations without the presence of an actual patient. Such a system would allow trainees to learn at an optimal location, time, and pace, and under standardized conditions. Trainees could thereby be exposed to an appropriate variety of pathologies, be they common or rare. Furthermore, such a system would allow for standardized and objective testing of trainee sonographers.